Here are a few cookie-baking tips I've culled over the years:
For the most even baking, bake cookies one sheet at a time, on the middle rack of the oven.
Watch cookies as the end of their baking time nears. Most finish quickly, and they can darken (read burn) quickly.
Cookies lend themselves to baking ahead and freezing. For best results, wrap the cookies up to three together -- and seal them in a container or resealable plastic freezer bag. Wrapping cookies this way before freezing them takes minutes and adds tremendous protection against their becoming stale and picking up unwanted odors. Be sure to defrost cookies with their wrapping on, so any moisture that forms is on the wrapper, not the cookie.
-- Elinor Klivans